STONE (1) and Beach (2) reported the execution of elements in the feminine copulatory pattern by male rats which were vigorous copulators in the normal masculine fashion. Various lines of evidence suggest the possibility that male rats possess neural mechanisms capable of mediating the mating behavior of the opposite sex, and that this overt behavior pattern may be manifested when the male, in a high state of sexual excitement, is repeatedly mounted and palpated by a vigorous copulator of his own sex. Arousal of sexual behavior in prepubertally castrated male rats after administration of testosterone propionate (3), and restoration of mating in postpubertal castrates by the same method (4) indicates that sexual excitability adequate to the occurrence of normal mating is dependent upon androgenic substances. Beach (5) found that sexually inexperienced male rats injected with testosterone propionate prior to opportunity for intercourse with the receptive female displayed a tendency to mate with non-receptiv...